Liquid crystal display devices are being used in watches, calculators, various measurement instruments, automobile panels, word processors, electronic organizers, printers, computers, televisions, clocks, advertising boards, etc. Typical examples of the liquid crystal display mode include TN (twisted nematic) mode, STN (super twisted nematic) mode, a VA mode featuring vertical alignment using TFTs (thin film transistors), and an IPS (in-plane switching) mode/FFS mode featuring horizontal alignment. Liquid crystal compositions used in these liquid crystal display devices are required to be stable against external factors such as moisture, air, heat, and light, stay in a liquid crystal phase in a temperature range as wide as possible centered around room temperature, exhibit low viscosity, and operate at a low drive voltage. A liquid crystal composition is composed of several to dozens of compounds in order to optimize the dielectric anisotropy (Δ∈), refractive index anisotropy (Δn), and other properties for individual display devices.
A vertical alignment-mode display uses a liquid crystal composition having a negative Δ∈. A horizontal alignment-mode display such as a TN, STN, or IPS-mode display uses a liquid crystal composition having a positive Δ∈. In recent years, a drive mode with which a liquid crystal composition having a positive Δ∈ is vertically aligned under absence of applied voltage and an image is displayed by applying an IPS/FFS-mode electric field has been reported and the necessity for a liquid crystal composition having a positive Δ∈ is increasing. Meanwhile, low-voltage driving, high-speed response, and wide operation temperature range are required in all driving modes. In other words, Δ∈ that is positive and has a large absolute value, a low viscosity (η), and a high nematic phase-isotropic liquid phase transition temperature (Tni) are desirable. Moreover, due to the setting of Δn×d, which is the product of Δn and a cell gap (d), it is necessary to adjust the Δn of the liquid crystal composition to be within an appropriate range according to the cell gap. In addition, since high-speed response is important in applying a liquid crystal display device to a television or the like, a liquid crystal composition with a small γ1 is required.
Liquid crystal compositions that use compounds having a positive Δ∈ and represented by formula (A-1) or (A-2) as the constitutional components of liquid crystal compositions have been disclosed (PTL 1 to PTL 4). However, these liquid crystal compositions do not achieve sufficiently low viscosity.
